Acidity (pH) (part 1)

Acidity, hereinafter referred to as pH, is one of the most important water parameters to monitor. pH is a Latin abbreviation of pondes Hydogenia, which means something like the force or weight (pondes) of hydrogen (Hydrogenia). You can easily imagine that hydrogen is powerful when you consider that cars can run on it and that it's even used to make atomic bombs. The chemical name for hydrogen is H+. So, when you measure pH, you're actually measuring the amount of H+.

Scale division

The pH scale ranges from 0 to 14. I'll spare you the reasoning, but what's important to know is that a pH of 0 is extremely acidic and a pH of 14 is extremely basic (or alkaline). For example, a bottle of hydrochloric acid has a pH of 1 (depending on the concentration), while drain cleaner quickly exceeds 13. A pH of 7 (right in the middle of the scale) is considered neutral (neither acidic nor alkaline). The scale is misleading in two ways:

First, if we find something very acidic, we tend to say it has a high acidity, which might lead you to think that something becomes more acidic as the pH increases. However, the exact opposite is true. As the pH decreases, the water becomes more acidic.

Second, we need to consider that the scale is logarithmic. A one-point decrease in pH makes the water 10 times more acidic. A two-point decrease in pH makes the water 100 times (10x10) more acidic. And so on. If you think a one-point drop in pH is fine ("oh, it's only one point"), you're actually down. A factor of ten has a huge impact!

The influence of Hydrogen

As mentioned, pH measures the influence of hydrogen (H+) in the water. It's essentially the ratio of H+ to OH-. An increase in H+ means a decrease in pH. Hydrogen therefore has an acidifying effect on the pond. A decrease in H+ therefore means an increase in pH. At a pH of 7, there are an equal number of H+ ions and OH- ions in the water.

In the article about Regarding nitrification, I indicated that the conversion of ammonia via nitrite to nitrate releases a lot of H+. The action of our biological filter therefore causes the water to become more acidic. I described exactly how this works in the KH article . We will therefore need to replace sufficient water to maintain the KH level and thus prevent a drop in pH (pH crash).

The ideal pH
Our pond fish prefer a pH between 7 and 8, and it's crucial that it remains stable throughout the day. A pH below 5 is fatal for most pond fish. This also applies to a pH above 10. Therefore, we strive for a stable pH between 7 and 8. I'll describe how to achieve this in a future article.

Author: Joop van Tol (www.koitoday.nl)